Clinical and laboratory studies are conducted to determine etiology (infection, immunity and/or genetics) for chronic diseases of the central nervous system. Current studies include Multiple Sclerosis, Progressive Multifocal Leukoencephalopathy, Subacute Sclerosing Panencephalitis, Myasthenia Gravis, Amyotrophic Lateral Sclerosis and Parkinson's Disease. Combined clinical data, genetic information, HLA and MLC typing, virus serology and virus isolation studies are obtained for these studies. Oligoclonal IgG was found in the CSF of 90% of MS patients, 90% of SSPE, 100% of patients with biopsy proven herpes simplex encephalitis and 50% of the patients with Myasthenia Gravis. No unusual antibody levels of oligoclonal IgG patterns were found in the serum or cerebrospinal fluid of patients with Parkinson's disease, Huntingon's disease or Creutzfeldt-Jakob disease. Previously unrecognized as a possibility the human-to-human transmission of rabies by corneal transplant was demonstrated. Donors with neurological diseases must be carefully reviewed before their tissue is used in transplantations.